Early in the war, on 3 September 1939, U-14 attacked a Polish submarine and claimed to have sunk it. In reality the Polish submarine, , was not damaged as the torpedo launched by U-14 exploded prematurely.

After serving six operational patrols, U-14 was used as a training boat, and transferred to U-boat training flotillas, serving with 23rd U-boat Flotilla and 24th U-boat Flotilla until the end of the war. Despite the high casualties suffered by the Unterseebootwaffen (German submarine arm), U-14 suffered no known casualties during the War. U-14 was scuttled on May 2, 1945 at Wilhelmshaven.